Porphyry edited the writings of Plotinus in fifty-four treatises, which vary greatly in length and number of chapters, mostly because he split original texts and joined others together to match this very number. Then, he proceeded to set the fifty-four treatises in groups of nine (Greek. ennea) or Enneads. He also collected The Enneads into three volumes. The first volume contained the first three Enneads (I, II, III), the second volume has the Fourth (IV) and the Fifth (V) Enneads, and the last volume was devoted to the remaining Enneads. After correcting and naming each treatise, Porphyry wrote a biography of his master, Life of Plotinus, intended to be an Introduction to the Enneads.

Porphyry's edition does not follow the chronological order in which Enneads were written (see Chronological Listing below), but responds to a plan of study which leads the learner from subjects related to his own affairs to subjects concerning the uttermost principles of the universe.

Although not exclusively, Porphyry tells us (Cf. Life of Plotinus, chapters.24-26) that the First Ennead deals with Human or ethical topics, the Second and Third Enneads are mostly devoted to cosmological subjects or physical reality, the Fourth concerns the Soul, the Fifth knowledge and intelligible reality, and finally the Sixth covers Being and what is above it, the One or first principle of all.

Since the publishing of a modern critical edition of the Greek text by P. Henry and H.-R. Schwyzer (Plotini Opera. 3 volumes. Paris-Bruxelles, 1951-1973) and the revised one (Plotini Opera. 3 volumes. Oxford: Clarendon Press, 1964-1984) there is an academic convention of quoting the Enneads by first mentioning the number of Ennead (usually in Romans from I to VI), the number of treatise within each Ennead (in arabics from 1 to 9), the number of chapter (in arabics also), and the line(s) in one of the mentioned editions. These numbers are divided by dots, by commas or blank spaces (there is no absolute consensus about this).

E.g. For Fourth Ennead (IV), treatise number seven (7), chapter two (2), lines one to five (1-5), we write:

IV.7.2.1-5

E.g. The following three mean Third Ennead (III), treatise number five (5), chapter nine (9), line eight (8):

III, 5, 9,8

3,5,9,8

III 5 9 8

It is important to remark that some translations or editions do not include the line numbers according to P. Henry and H.-R. Schwyzer’s edition. In addition to this, the chronological order of the treatises is numbered between brackets or parentheses, and given below.

E.g. For the previously given:

IV.7 (2).2.1-5 since treatise IV.7 was the second written by Plotinus.

The names of treatises may differ according to translation. The numbers in square brackets before the individual works refer to the chronological order they were written according to Porphyry's Life of Plotinus.

After the fall of Western Roman Empire and during the period of the Byzantine Empire, the authorship of some Plotinus' texts became clouded. Many passages of Enneads IV-VI, now known as Plotiniana Arabica, circulated among Islamic scholars (as Al-Kindi, Al-Farabi and Avicenna) under the name The Theology of Aristotle or quoted as "Sayings of an old [wise] man". The writings had a significant effect on Islamic philosophy, due to Islamic interest in Aristotle. A Latin version of the so-called Theology appeared in Europe in 1519. (Cf. O'MEARA, An Introduction the Enneads. Oxford: 1995, 111ff.)